Generally, a terminal which supports a Universal Mobile Telecommunications System (UMTS) protocol amplifies weak signals of voice and data modulated, via an antenna, from a baseband chip by a specific level of power in order to establish a call connection with a base station.
A transmitting characteristic, by an impedance, of a RF signal through a power amplifier of the terminal changes significantly as a frequency increases. Thus, an impedance conformity is should be performed in operation between the power amplifier and the antenna.
The impedance conformity is performed at the terminal between the power amplifier and the antenna by using load pull (source-pull with respect to the signal source), which provides coupling a tuner to the input or output of the terminal and adjusting the tuner impedance while monitoring to find an optimum impedance in terms of output power, gain, and so forth. A transistor in the power amplifier outputs a maximum power when the optimum load impedance is used. The load pull measurements used in a conventional technology are determined by vendors of the power amplifiers. However, a test to the power amplifier is typically preformed using the load full measurements.
Normally, each communication channel has a similar characteristic in an identical phase as illustrated in FIG. 1. However, as illustrated in FIG. 2, because some elements between a power amplifier 201 and an antenna 205 exist in a real terminal, distorted load full measurements are produced when the load pull is only applied to the power amplifier.
Further, when only the load pull for the power amplifier is applied as in the conventional technology, because a Scattering parameter of the front end module 203 serves as a buffer, a Voltage Standing Wave Ratio (VSWR) is increased so that a deviation per channel increases as illustrated in FIG. 3.
Moreover, due to deviations of a power, a current, an Adjacent Channel Leakage Ratio (ACLR) and an Inner Loop Power Control (ILPC) are increased.
To address this problem, when the deviation per channel is occurred, a tuning is used in order to minimize the deviation by changing a fixed matching value of an output terminal of the power amplifier or by changing a fixed matching value of the antenna in the conventional art. However, when the conventional scheme is used, a trade off must be considered between parameters such as the power, the current, the ACLR and the ILPC in attempts to limit the interference level within the system. Hence, not all channels can achieve a desired quality of service with a minimum transmit power level.